Magnetic tape cartridges or cassettes (e.g., videocassettes) are ubiquitous. The magnetic tape in these cassettes is wound onto reels which are rotatably mounted within a housing. These cassettes typically includes a spring which is mounted to the housing and engages wear buttons on the axial centers of the reels. The spring applies axial pressure to the reels to insure proper engagement with the drive spindle of the cassette drive. It also prevents the reels from being jostled around when the cassette is transported.
One of the specifications of VHS videocassettes requires that the reel pressure spring provide a loading or pressure of between 280 and 380 grams when the spring ends are depressed to a distance of approximately 0.080 inches from the spring mounting surface (an inside wall of the cassette).
One spring is a stainless steel strip which is fastened at the center to the inner surface of an upper housing wall. The free ends of the strip are bent into upwardly opening arcs away from the housing wall. The free ends are cantilevered from the center portion of the strip and resiliently engage, adjacent their outer ends, the hubs of the reels to bias the reels away from the upper housing wall. Since the force exerted by this type of reel spring on the housing wall can be significant, the housing wall must be sufficiently strong, and hence sufficiently thick, to withstand the reel spring force without excessive deformation.
There is a continuing need for improved reel springs for videocassettes which place a lower demand upon the structural strength of the cassette cover to allow the use of thin-walled cassette covers while meeting the specifications and reducing cost. Because videocassettes are produced in high volumes, small changes in piece part costs can have a large effect upon overall production costs. For this reason, improvements resulting in even a small reduction in a piece part cost can result in significant improvements in the commercial viability of the product.